I have a 3 ton basement AC I am ready to install. The unit does not require recirulation of the interior air but I am thinking it might be better than dirty outside air or worse yet air not previously cooled. I am considering placing two or three floor registers on each side of the middle bay and using that closed system for air recirculation. The middle bay would provide more that enough air flow. The registers would be lovered so during non-function would be closed. The unit needs about 420 square inches of air flow to make if function correctly.

Any of you out there tried this? Is so, ideas would be greatly appreciated. I am not going to install roof airs at this time. I may even consider another basement unit in the future. MCI 9.

I have done exactly what you are sugesting,return air in the raceway in the middle works just fine my unit is only 2 ton and will bring down the temp from 100 deg. down to 75 deg in about 15 min cold air ducts in the ceiling, 4 - 4x12 floor registers in the floor .Insulation is the key!!!

Merlin, when you say insulation, do you mean on the duct work or the entire bus. I am not doing a complete conversion at this time so am somewhat dependent on system keeping the bus comfortable. I may add a second unit if needed. I do have the OTR AC system that still works.

Thanks for the input. Any pictures of the system would be greatly appreciated both interior and exterior.

Nick, thanks for the quick reply. I sent a response but it looks like it did not make it. I have looked over your Yahoo site and have a few more detailed questions. I have my single ac unit on a sliding joey bed. It sits on the curb side middle bay. I have the condenser coils facing outwards. I would like to build a manifold that encloses the air being pulled from the floor of the coach pass the coils and then like you have the supply air discharge in two ducts for each side of the bay. The condenser coil side is 35 inches wide. I cannot see a hole in the floor that large? How did you open enough floor space to get the air flow. The manual suggests 420 inches of unrestricted air flow for maximum efficiency. I was thinking three or four 6x12 registers and then one or two allowing bay air to enter in as well. Any ideas? Also, I am not doing a complete tear out of the interior at this point so no overhead duct work. Should I just return the cold air via floor registers as well?

Hopefully this isn't a repeat question. Thanks again for your time and expertise.

I would reconsider pulling air from inside a bay, You will be pulling dirty, odors and all kinds of creepy stuff in through air leaksin the plumbing and electrical tunnel. Have you looked in there at the coat of SOOT? It gets sucked from the engine bayall the way up into the stock a/c air intake if any of the rubber seals are missing.

Also if you have any pass through holes between the bays you may also be pulling a negative pressure in them as well andthere is a lot of stinky stuff down there that honestly you wouldn't be happy about smelling.